1. Field of the Invention
The present invention relates, in general, to vehicle windshield wiper systems and, more specifically, to control of the wipe pattern at extreme end limits of wiper travel.
2. Description of the Art
Vehicle windshield wiper systems of the type in which the windshield wiper blade direction is reversed, for example, tandem, symmetrical overlap, single arm, single extending arm, etc., are widely known and are included as standard equipment on nearly every motor vehicle. Such windshield wiper systems typically include a dual speed drive motor that continuously rotates a crank arm. In order to translate the continuous rotation of the crank arm into the back and forth or oscillating sweeping action needed in a wiper, a linkage, such as a four bar linkage, connects the crank arm to the wiper arm.
The wiper arm is oscillated back and forth between inner and outer end wipe limits determined by the dimensions of the links of the various arms of the linkage, often with a large mechanical advantage at certain portions of the 360xc2x0 rotation cycle of the crank arm. The inwipe and outwipe end limits of travel define the wipe pattern as the wiper operates.
Maintenance of a constant wiper speed or even an acceleration through the reversal points where the wiper arm and blade direction is reversed at the inwipe and outwipe end limits, produces several undesirable effects, including wipe pattern or angle growth, increased production of noise, and wear on the windshield wiper drive linkage and wiper arms, particularly at high speed motor operation. During such high speed motor operation, the wiper arm tends to travel past a nominal reversal point at least at the outwipe end limit, thus increasing the wipe angle or pattern, at least at the outwipe position. When the wiper arm and blade travel past the nominal outwipe limit to an extent that the wiper arm and blade contact a windshield pillar, the resulting xe2x80x9cslapxe2x80x9d or contact produces undesirable noise. This impact loading also has an adverse effect on the motor and linkage.
Although such noise is not necessarily a safety concern, the undesirable noise at high speed wiper arm operation adversely impacts customer perception of the quantity of the vehicle and/or the vehicle wiper system. Such perception is also impacted by the variability between the wipe pattern during low and high speed wiper motor operations.
Research in the development of vehicle windshield wiper systems shows that the inertial tendency of the wiper arm to keep moving in the direction that it is sweeping becomes a very significant contributing force to wipe pattern extension, particularly at high motor operating speeds.
Windshield wiper systems are known in which the wiper position is sensed and a switching mechanism employed to slow the motor just prior to the reversal of the blade and arm directions at the inner and outer end wipe positions. In such systems, even though the wiper motor is normally operated at a high speed for the most of the wipe pattern or sweep, as the wiper arm and blade approach the inwipe or outwipe end limits, the switching circuit switches the motor to a low speed to provide a soft wipe mode at the inwipe and outwipe reversal points.
However, it is believed that it would be desirable to provide an improved windshield wiper system which is capable of minimizing wipe pattern expansion, especially under high speed wiper motor operation. It would also be desirable to provide an energy absorption apparatus for minimizing wiper pattern expansion which can be adapted for use in many different windshield wiper arrangements.
The present invention is an apparatus and method for absorbing a portion of the inertial energy of a moving wiper in a windshield wiper apparatus as the wiper arm approaches and moves away from one of the inwipe and outwipe end limits of travel in the wipe pattern.
In one aspect of the invention, a windshield wiper apparatus for a vehicle comprises:
a pivot housing fixed to the vehicle;
a pivot shaft carried within the pivot housing and capable of rotation about the longitudinal axis over a predetermined angle defining a wipe pattern;
a wiper arm rotatably mounted on the pivot shaft and movable in the wipe pattern between an inwipe end limit and an outwipe end limit;
a drive motor having a drive shaft rotatable about a drive axis;
a crank arm coupled to the motor drive shaft at one end for rotation with the motor drive shaft;
a drive link having a first end pivotally connected to a drive arm and a second end coupled to the crank arm for bidirectional oscillation upon rotation of the crank arm, the drive arm fixedly connected at one end to the pivot shaft for bidirectional rotation of the pivot shaft upon oscillation of the drive link; and
energy absorption means, coupled to the drive arm, for storing a portion of the inertial energy of the wiper arm as the wiper arm moves toward at least one of the inwipe end limit and the outwipe end limit.
In one aspect of the invention, the energy storage means also releases the stored energy to the wiper arm, the drive arm and the drive link as the wiper arm begins movement from the one end limit toward the other end limit.
In another aspect of the invention, the energy absorption means is a spring connected between the drive arm and stationary vehicle structure, such as the pivot housing, for storing energy as the wiper arm approaches at least one of the inwipe and the outwipe end limits.
In a specific aspect, the spring is an extension spring which extends to store energy as the wiper arm approaches one of the end limits.
In another aspect, the spring is a coil tension spring concentrically mounted about the pivot housing and having opposed ends connected to the drive arm and to stationary structure, respectively.
In yet another aspect, the spring is a leaf spring fixed at a first end to the drive arm and having a flexible second end extending from the first end. A projection extends from the pivot housing and engages and flexes the second end of the leaf spring during movement of the drive arm to store energy in the leaf spring.
In yet another aspect of the invention, the energy absorption means is a resilient, compressive member carried on the pivot housing and engagable with a flange on the drive arm so as to be compressed during movement of the drive arm toward one of the end limits of travel.
The energy absorption means is unidirectionally operative upon movement of the wiper arm toward one of the inwipe and outwipe end limits of travel. The energy absorption means can also be devised for bidirectional operation at each of the inwipe and the outwipe end limits.
In one aspect, the energy absorption means is devised to begin providing an opposed force and absorbing inertial energy from the wiper arm at the point in the angular travel of the drive arm which coincides with the significant ramp up or increase in the mechanical advantage in the wiper linkage on the drive arm. In this aspect, one end of the spring is movably disposed in a slot in a flange on the pivot housing. While one end of the spring moves from one end to the other end of the slot, the spring is unable to store of energy during a portion of the travel of the wiper arm across the wipe pattern. However, the engagement of one end of the spring with one end of the slot which coincides with the start of the mechanical advantage area, enables the spring to begin to store energy.
In another aspect of the invention, a method of storing inertial energy during a portion of the wipe pattern of a wiper arm in a vehicle windshield wiper apparatus is disclosed.
In this aspect of the invention, the method includes the step of coupling an energy absorption means between the drive arm and a stationary element for storing a portion of the inertial energy of the moving wiper arm as the wiper arm moves approaches at least one of the inwipe end limit and the outwipe end limit.
In another aspect of this method, the energy absorption means is also devised for releasing energy back to the drive arm after the wiper arm reverses its direction of travel at one of the outwipe or inwipe end limits.
In yet another aspect of the inventive method, the method includes the step of connecting the energy absorption means for unidirectional operation at only one of the inwipe and outwipe end limits. Alternately, the energy absorption means is connected for bidirectional operation in storing inertial energy as the wiper arm approaches each of the inwipe and outwipe end limits.
The present inventive apparatus and method provides a means for minimizing expansion of the wipe pattern in a vehicle windshield wiper apparatus, particularly at a high speed wiper motor operation, or reducing the outwipe angle difference between low speed and high speed wiper motor operation. In the present invention, an energy absorption means is connected between a fixed, stationary part of the wiper apparatus or the vehicle and the movable drive arm for presenting an opposing force capable of storing or diverting a portion of the inertial energy of the wiper arm as the wiper arm approaches one of the end limits of travel in the wipe pattern. This stored energy is subsequently returned to the drive arm to assist in accelerating the drive arm after the wiper arm reverses direction at one of the end limits of travel in the wipe pattern.
The unique energy absorption means of the present invention reduces noise caused by reversal of the wiper arm at the outwipe position where the wipe pattern has been extended at the outwipe position due to increased inertial energy of the wiper arm at high speed motor operation. The energy absorption means of the present invention also reduces impact loading on the motor and the entire wiper linkage by reducing acceleration of the wiper arm and linkage going into wiper arm reversal at the end limits of the wipe pattern.